In a fuel cell, electricity is produced from chemical fuels. Voltage is generated by portable hydrogen-air fuel cells when hydrogen and compressed air are separately introduced into the cell. A major use of hydrogen-air fuel cells is in remote areas where no other source of electricity is available. Fuel cells are also used in transportation vehicles where hazardous environments dictate the absence of spark plugs and the typical internal combustion engine.
Fuel cells are used to provide either direct or alternating current to small vehicles, to field equipment and for navigation lights. These fuel cells are manufactured in different sizes: small units portable by one person as well as very large units capable of serving as commercial power plants. The small units commonly have useful lives on the order of 5000 hours; those constructed to serve as commercial power plants are designed to last for periods as long as ten to twenty years.
One type of hydrogen-air fuel cell operates at temperatures of about 200.degree. C. and utilizes concentrated phosphoric acid as the electrolyte. The various structural components of this type of fuel cell must withstand this harsh hot acid environment for months or years.
The hydrogen-air fuel cell is made using conventional parts: current collecting plates, electrodes, a matrix membrane separator and an electrolyte. The matrix membrane separates the gas flows to the cathode and to the anode. Mixing of the gases is prevented and is essential to long term use of the fuel cell. The current collecting plates are bipolar plates used to connect adjacent cells in a stack of numerous cells. These bipolar plates distribute the incoming gases around the electrodes and provide rigidity. The plates are made of graphite powders bonded together by an organic polymer resin. The graphite provides the requisite conductivity.
All of the parts of the fuel cell must withstand the 200.degree. C. operating temperature and the phosphoric acid electrolyte. Long term mechanical integrity of the matrix membrane and bipolar collecting plates is essential to prevent mixing of the air and hydrogen. In the past, bipolar plates prepared using conventional techniques could not meet the essential requirements of electrical conductivity, hydrogen impermeability and long term mechanical strength.